The sum of two positive integers is 50 and their difference  is 12. What is the value of the positive difference of the squares of the integers?
Answer: Call the two integers $x$ and $y$. Without loss of generality, let $x$ be the larger of the two. We are given that $x+y = 50$ and $x-y = 12$, and we are asked for $x^2 - y^2$. Because $x^2 - y^2$ factors into $(x+y)(x-y)$, we can simply substitute in to get $x^2 - y^2 = 50 \cdot 12 = \boxed{600}$.